L.-P. Demay was sponsored as master by Louis Lenhendrick in 1758, when he was living on the pont Notre-Dame in Paris. In 1769 he sponsored his son, Jacques-Joseph Demay, as master. In the same year a watch-case was seized from L.-P. Demay by the wardens of the guild as being below standard, but it was subsequently returned to him. His shop on the pont Notre-Dame was at the sign of the Golden Hawthorn but he had moved to quai de Conti when he died in 1772. His widow continued the business at least until 1774. The enameller Charles-Jacques de Mailly seems to have worked for him before leaving for Moscow.